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This invention relates to a chemical vapor deposition process for depositing copper films on barrier layer materials, and more specifically, to improving adhesion between copper and barrier layers.
CVD (Chemical Vapor Deposition) is a superior process for producing microscopic metal features on substrates. In this technique, a volatile metal-organic compound in the gas phase is contacted with areas of a circuit where growth of a metal film (e.g., an interconnect) is required.
Copper films have previously been prepared via CVD using various copper precursors. One of the best known and most frequently used CVD copper precursors is the solid compound copper+2 bis(hexafluoroacetylacetonate) (i.e., copper+2 bis(hfac)). This highly fluorinated organometallic precursor is significantly more volatile than its parent unfluorinated complex, copper+2 bis(acetylacetonate), and its ease of vaporization has made it a popular choice for CVD processes. The use of this compound as a general precursor for CVD copper metallization was first described by Van Hemert et al. in J. Electrochem. Soc. (112), 1123 (1965) and by Moshier et al. in U.S. Pat. No. 3,356,527. More recently, Reisman et al. (J. Electrochemical Soc., Vol. 136, No. 11, November 1989) and Kaloyeros et al. (Journal of Electronic Materials, Vol. 19, No. 3, 271, 1990) in two independent studies evaluated the use of this compound as a copper precursor for electronics applications. In these studies, copper films were formed by contacting vapors of copper+2(hfac)2, mixed with either an inert gas (argon) or hydrogen and contacting the mixture with a heated substrate surface. In the case of using hydrogen, the copper+2 atom in the precursor complex is formally reduced to copper metal, while the hfacxe2x88x921 ligand becomes protonated to yield a neutral volatile compound. In the case of using an inert gas, the copper+2 (hfac)2 is simply pyrolyzed to give copper metal and fragments of the hfac ligand.
Selective deposition of pure copper films by CVD at low temperatures onto metallic substrates using Cu+1 (hfac)L complexes (where L is alkene or alkyne) has been described previously by Norman et al. in U.S. Pat. Nos. 5,085,731, 5,094,701 and 5,098,516. Under certain conditions, blanket (non-selective) deposition can also be achieved using these precursors (Norman et al., E-MRS proc. B17 (1993) 87-92). A particularly effective CVD copper precursor is 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato-copper (I) trimethylvinylsilane (hereinafter Cu(hfac)(TMVS)), which is sold under the trademark CupraSelect by the Schumacher unit of Air Products and Chemicals, Inc., Carlsbad, Calif.
As shown by the following equations, precursors such as Cu(hfac)(TMVS) function by a surface catalyzed disproportionation reaction to give a volatile Cu+2 complex, free olefin and copper metal (wherein (s) denotes interaction with a surface and (g) denotes the gas phase):
xe2x80x832 Cu+1hfacTMVS(g)xe2x86x922 Cu+1hfacTMVS(s)xe2x80x83xe2x80x83(1)
2 Cu+1hfacTMVS(s)xe2x86x922 Cu+1hfac(s)+2 TMVS(g)xe2x80x83xe2x80x83(2)
2 Cu+1hfac(s)xe2x86x92Cu(s)+Cu+2(hfac)2(g)xe2x80x83xe2x80x83(3)
In Equation (1), the complex is adsorbed from the gas phase onto a metallic surface. In Equation (2), the coordinated olefin (TMVS in this example) dissociates from the complex as a free gas leaving behind Cu+1hfac as an unstable compound. In Equation (3), the Cu+1hfac disproportionates to yield copper metal and volatile Cu+2(hfac)2.
Despite the foregoing developments, the integrated circuit (IC) industry is presently experiencing difficulty forming adherent copper films on barrier layer materials such as Ta, TaN, TiN, etc., via chemical vapor deposition (CVD) with fluorinated precursors, including hfac-based precursors such as Cu(hfac)(TMVS). A variety of solutions to this problem have been proposed.
For example, Gandikota et al., 50 Microelectronic Engineering 547-53 (2000), purports to improve adhesion between a CVD copper thin film and barrier layers by: (a) depositing a copper flash layer on the barrier layer by physical vapor deposition (PVD) prior to chemical vapor deposition, or (b) annealing the CVD copper layer after deposition. See also Voss et al., 50 Microelectronics Engineering 501-08 (2000). Unfortunately, these methods are not acceptable to the IC industry because they add to the equipment requirements for the copper deposition step. In addition, annealing, particularly at elevated temperatures, can have deleterious effects on the overall product.
WO 00/03420 (Paranjpe et al.) discloses improving CVD copper adhesion to a diffusion barrier layer by: (a) annealing the seed layer deposited on the diffusion barrier layer surface, or (b) providing an inert seed layer (e.g., comprising a noble or passivated metal) on the diffusion barrier layer surface.
WO 99/63590 (Bhan et al.) discloses improving CVD copper adhesion to a diffusion barrier layer by: (a) providing a copper seed layer containing water on the diffusion barrier, and (b) annealing the seed layer with heat or ion bombardment.
U.S. Pat. No. 5,909,637 to Charneski et al. discloses a copper CVD method comprising exposing a surface of a diffusion barrier layer to a reactive gas species to purportedly replace high-energy molecular bonds on the surface with low-energy bonds between the reactive gas species and the surface. This is said to change the surface characteristics of the exposed copper-receiving surface to promote the formation of bonds between the copper-receiving surface and copper subsequently deposited by CVD, whereby copper adhesion to the diffusion barrier is improved. The low-energy bonds are said to promote the adhesion of copper to the diffusion barrier layer.
U.S. Pat. No. 5,913,144 to Nguyen et al. discloses a process for improving adhesion of CVD copper to barrier layers, comprising the steps of: exposing the copper-receiving surface to a reactive oxygen species; oxidizing a thin layer of the diffusion barrier material surface in response to the oxygen exposure; and stopping the exposure of the diffusion barrier material to the oxygen before the oxide layer exceeds approximately 30 angstroms, whereby the relatively thin oxide layer prepares the diffusion barrier material receiving surface for adhesion to copper.
U.S. Pat. No. 5,918,150 to Nguyen et al. discloses the use of an inert gas to remove contaminating byproducts of the disproportionation reaction which deposits copper on the diffusion barrier layer. Low energy ions of the inert gas are impinged upon the contaminated copper layer to physically displace contaminants thereon and provide a clean copper surface for additional copper CVD.
U.S. Pat. No. 5,948,467 to Nguyen et al. discloses a two-step deposition process, wherein the first step comprises copper CVD at a low deposition rate and the second step comprises copper CVD at a high deposition rate. The initial slow deposition rate is said to allow organic solvents within the precursor vapor to be carried out of the process chamber instead of being captured within the film at the interface between the diffusion barrier layer and overlying CVD copper. This is said to provide improved adhesion of CVD copper to the underlying diffusion barrier layer.
U.S. Pat. No. 5,953,634 to Kajita et al. discloses a two-step deposition process, wherein the first step comprises copper CVD in the presence of an oxidizing gas and the second step comprises copper CVD in the absence of the oxidizing gas.
JP-A-10-98043 (Nguyen et al.) discloses a method for oxidizing the surface of the to diffusion barrier layer to improve CVD copper adhesion thereto.
U.S. Pat. No. 6,015,749 to Liu et al. discloses improving CVD copper adhesion to diffusion barrier layers by implanting germanium ions in a copper seed layer deposited on the diffusion barrier layer surface.
In addition, the inventors filed on Aug. 15, 2000 U.S. patent application Ser. No. 09/638,586, which discloses improving CVD copper adhesion to diffusion barrier layers by treating a diffusion barrier layer surface and/or a deposited film with a donating molecule selected from the group consisting of a proton-donating molecule and a hydrogen-donating molecule (e.g., methylsilane).
Although the inventors are aware of references teaching the use of certain halogen-containing molecules in microelectronic processing, these references do not disclose the use of halogen-containing molecules to improve CVD copper adhesion to barrier layers. For example, U.S. Pat. No. 5,599,425 to Langendijk et al. discloses the use of certain organic chlorides in silicon processing, but does not teach that depositing copper on a barrier layer in the presence of a halogen-containing molecule can improve adhesion of the copper to the barrier layer.
Hwang et al., 3(3) Electrochemical and Solid-State Letters 138-40 (2000) discloses that certain iodine-containing molecules, including ethyl iodide, methyl iodide, tertiary-butyl iodide and molecular iodine, can minimize the roughness of surfaces deposited by copper MOCVD. The resulting films are said to be predominantly (111)-oriented, regardless of the deposition conditions, provided that iodine is adsorbed to the growing film surface. Hwang et al. does not disclose that halogen-containing molecules can improve the adhesion of the copper to a barrier layer.
Despite the foregoing developments, there remains a need in the art for alternative solutions to the CVD copper adhesion problem.
All references cited herein are incorporated herein by reference in their entireties.
Accordingly, the invention provides an improved copper CVD process, wherein the improvement comprises treating at least one of the surface and the copper film with an adhesion-promoting agent comprising a halogen other than fluorine, and annealing the copper film to the surface. The inventive process provides copper-based films, wherein a texture of the copper-based films is predominantly (111). Such films provide substrates having enhanced adhesion between the diffusion barrier layer underlying the (111) film and the copper overlying the (111) film.